U.S. patent number 5,865,338 [Application Number 08/823,211] was granted by the patent office on 1999-02-02 for method for adding strength to a container.
This patent grant is currently assigned to Rubbermaid Incorporated. Invention is credited to Wendell Conn.
United States Patent |
5,865,338 |
Conn |
February 2, 1999 |
Method for adding strength to a container
Abstract
An improved method of blow molding a hollow article is disclosed
comprising the adaptation of a die pin (26) to include spaced apart
channels (38) therein that extend from top to bottom along the
sides of the die pin. The channels create reinforcement ribs (70)
along the inside surface (68) of a formed parison (30). The ribs
expand with the parison into a final form and serve to reinforce
the resultant body while being visible only from the inside. The
channels (38) are each bifurcated to provide a segment (44) below a
shut-off surface (46) in which plastic exiting the die pin can
expand to form ribs (70) of substantial thickness. Portions of the
parison sidewalls (66) between the ribs (70) are thinned to reduce
part weight and the ribs (70) reinforce the sidewalls to compensate
yet, being visible only from the inside, do not detract from the
external appearance of the article.
Inventors: |
Conn; Wendell (Polk, OH) |
Assignee: |
Rubbermaid Incorporated
(Wooster, OH)
|
Family
ID: |
25238097 |
Appl.
No.: |
08/823,211 |
Filed: |
March 24, 1997 |
Current U.S.
Class: |
220/675; 220/623;
220/908 |
Current CPC
Class: |
B29C
48/09 (20190201); B65F 1/16 (20130101); B65F
1/02 (20130101); B29C 49/0078 (20130101); B29C
48/0017 (20190201); B29C 49/04 (20130101); B29B
2911/1434 (20130101); B29C 48/0018 (20190201); B29C
48/12 (20190201); Y10S 220/908 (20130101); B29B
2911/14593 (20130101) |
Current International
Class: |
B65F
1/02 (20060101); B65F 1/16 (20060101); B29C
47/00 (20060101); B29C 49/00 (20060101); B29C
49/04 (20060101); B65D 045/00 () |
Field of
Search: |
;220/623,651,669,675,908 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Pp. 2 and 6, Internal surface of a container; Continental
Manufacturing Company, 123 Byassee Dr., Hazelwood, Missouri 63042.
Publication date Oct. 1994. .
Catalog Page, Internal surface of a container; hammerlit GmbH, 2762
Leer, Postfach 1228. Publication date Oct. 1995. .
Catalog Page, Internal surface of a container; Toter Incorporated,
P.O. Box 5338, 841 Meacham Road, Statsville, North Carolina 28677.
Publication date Apr. 1992. .
Catalog Page, Internal surface of a container; Rubbermaid
Incorporated, 1147 Akron Road, Wooster, Ohio 44691. Publication
date 1980. .
Catalog Page, Internal surface of a container; Rubbermaid
Incorporated, 1147 Akron Road, Wooster, Ohio 44691. Publication
date 1980. .
Catalog Page, Internal surface of a container; Schlosser & Co.,
GmbH, Industriestr. 22, 8062 Markt Indersdorf. Publication date
Dec. 1995. .
Catalog Page, Internal surface of a container; Rubbermaid
Commercial Products Inc., 3124 Valley Avenue, Winchester, Virginia
22601. Publication date 1992..
|
Primary Examiner: Pollard; Steven
Attorney, Agent or Firm: O'Planick; Richard B. Nathan;
Timothy A.
Claims
I claim:
1. A molded hollow container comprising:
a concave bottom panel and side panels that extend from the bottom
panel to an upper rim and define an internal chamber
therebetween;
spaced apart and inwardly directed reinforcement ribs integrally
formed with and projecting from inward surfaces of the bottom and
side panels into the chamber,
the ribs extend continuously downward from upper ends along the
inward surfaces of the side panels and continuously converge in
spaced apart relationship therefrom along the inward concave
surface of the bottom panel to terminal rib ends, the terminal rib
ends being located proximate each other at a central region of the
bottom panel, and the ribs having a relatively thick
cross-sectional dimension from the upper ends to the terminal ends
thereof; and
the bottom panel and side panels have connective portions between
the rib of relatively reduced cross-sectional dimension and of
substantially constant thickness downward along the side panels and
across the concave bottom panel.
2. A container according to claim 1, wherein the ribs extend
longitudinally along the inward surfaces of the side panels from
the upper rim downward and across the bottom panel.
3. A container according to claim 2, wherein the ribs of the
container are visible only to the inside of the side and bottom
panels.
4. A container according to claim 3, wherein further comprising a
lid component formed to have a top panel and a dependent skirt
portion that extends downward from the top panel to a lower
terminal edge, the lid fits over the upper rim of the container and
encloses the chamber; and
spaced apart and inwardly directed reinforcement ribs integrally
formed with and projecting from inward surfaces of the top panel
and skirt portion, and the ribs have a relatively thick
cross-sectional dimension; and
the lid top panel and skirt portions have connective portions
between the ribs of relatively reduced cross-sectional
dimension.
5. A container according to claim 4, wherein the ribs extend across
the top panel and downwardly along the inward surface of the skirt
portion to the lower terminal edge.
6. A container according to claim 5, wherein the ribs of the lid
are visible only to the inside of the top panel and the skirt
panels.
7. A container according to claim 6, wherein the lid and container
are unitarily molded of plastics material in adjacent relationship
from a single parison form, wherein the ribs of each of the lid and
the container are formed as continuous extensions of the ribs of
the other.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates generally to plastic blow molded containers
such as refuse containers and, more specifically, to methods of
reinforcing such articles to achieve enhanced strength
characteristics and reduced cost of manufacture.
2. The Prior Art
The blow molding process is commonly used in the production of
containers for various applications. For example, many commercially
available refuse containers, comprising a lid and a base, are
manufactured by such a process. Conventional blow molding apparatus
manufacture containers by means of blow molding from tubular
preforms or parisons which are extruded of plastic by extruder
heads from plastics material which has been plasticized in
extruders. The discharge nozzle from which the platicized material
exits to create the preform typically includes a die ring having a
center aperture and a frustro-conical die pin that is received into
the die ring aperture. The spacing between the outer surfaces of
the die pin and the outward directed surfaces of the die ring which
define the aperture is adjustably controlled by movement of the die
pin in and out of the die ring.
From the extruder, plastic is pressured downward between the die
pin and the die ring, forming a hollow parison which is suspended
between two mold halves. The parison is then expanded outwardly by
the injection of air into the center and reforms against the mold
sidewalls. The air can be injected from the top through the die pin
or, alternatively, from the bottom of the mold cavity. After the
plastic sets against the mold sidewalls, the mold is open and the
hollow article formed thereby is extracted.
U.S. Pat. Nos. 4,889,477 and 4,297,092, incorporated herein by
reference, illustrate the general state of the art apparatus for
blow molding hollow objects. The process works well and may be used
to form hollow bodies for a variety of applications. For example,
Design U.S. Pat. No. 326,342 shows a refuse container that is
preferrably formed by a gas-assisted molding technique. The
container comprises a lid and a base, both integrally formed from
the same parison. Subsequent to the molding operation, the lid and
the base are severed into independent components. An advantage to
forming articles by this method is that the walls of the container
and lid can be thinned to a great degree, thereby conserving
plastic and reducing costs. However, in making the walls of thinner
stock, the container and base can lose its structural rigidity and
integrity. The resultant product, while functional for its intended
purpose, can be perceived as being structurally inferior to
containers formed by other means.
To compensate for reduced rigidity resulting from thinning the wall
stock, designers of containers have incorporated shoulders and
recesses into the external wall surface. These structural elements
are effective in increasing the hoop strength and rigidity of the
containers. However, forming shoulders and recesses into the
sidewalls can detract from the aesthetic appeal of the exterior of
the container and limits design alternatives.
SUMMARY OF THE INVENTION
The subject invention overcomes the aforementioned deficiencies in
state of the art blow molding techniques and containers made
thereby. The die pin in the parison forming ejector is adapted to
have spaced apart channels extending along outward surfaces,
aligned in the direction of plastic material flow. Each channel
tapers upward at a lower end to a cutoff surface and includes a
channel segment at the opposite side of the cut-off surface at the
lower end of the die pin. The lower portions of the channels allow
space for the material to expand once it leaves the die pin,
allowing for the formation of thicker ribs than otherwise
possible.
The formation of the parison proceeds as described above, with
molten plastic pressurized over the die pin outward surfaces to
exit in the form of the hollow parison. The channels within the die
pin outward surfaces forms ribs extending internally along the
parison from a top end to a bottom end. Subsequent expansion of the
parison outward against the mold accordingly creates a part that
has ribs extending internally therealong from top to bottom. These
ribs are of greater sectional thickness than connective wall stock
therebetween, and give enhanced rigidity to the molded part.
In the preferred embodiment, the molded part is a container that
includes integrally formed lid and base components. The ribs extend
along the inward surfaces of the lid and base and are apparent only
from the inside. The ribs are of greater sectional thickness than
the nominal stock thickness in a conventional container, but the
connective wall stock therebetween can be made to be of
substantially thinner stock. The result is a net reduction in
plastic weight in the part, yet a part that has greater hoop
strength and rigidity than a conventionally formed container.
Finally, the container and lid can have any external appearance
desired since the ribs are only visible from inside. Thus, the
aforementioned constraints on design due to strength considerations
have been eliminated.
Accordingly, it is an objective of the present invention to provide
an improved method for producing, by blow molding, a product having
a reduced part weight yet increased structural rigidity and
strength.
Another objective is to provide a reinforced molded container and
method of manufacture thereof in which the means of reinforcement
are not externally visible.
Yet a further objective is to provide a base receptacle and lid
integrally formed from a common parison and having common strength
reinforcing means.
An objective of the invention is to provide an improved method for
producing and, by a blow molding process, a reinforced container
that has reduced part weight, reduced material consumption, and
increased strength.
A further objective is to provide an improved method for producing
a reinforced container by a blow molding process that is no less
efficient than state of the art methods.
Another objective is to provide improved blow molding apparatus
that is inexpensive to manufacture and can be easily and readily
retrofitted to existing equipment.
Still another objective is to provide an improved die pin
configuration capable of forming relatively thick ribs along the
inside surface of a hollow parison.
These and other objectives, which will be apparent to those skilled
in the art, are achieved by a preferred embodiment that is
described in detail below and illustrated in the accompanying
drawings.
DESCRIPTION OF THE ACCOMPANYING DRAWINGS
FIG. 1 is a perspective view of a refuse container produced
pursuant to the subject invention.
FIG. 2 is an exploded perspective view of a die pin, die ring, and
parison formed thereby pursuant to the invention.
FIG. 3 is a top plan view of the assembled die pin and die
ring.
FIG. 4 is a bottom plan view of the die pin.
FIG. 5 is a transverse section view through the assembled die pin
and die ring, taken along the line 5--5 of FIG. 3.
FIG. 6 is an enlarged section view through the assembled die pin
and die ring in the open configuration, taken along the line 6--6
of FIG. 3.
FIG. 7 is an enlarged section view through the assembled die pin
and die ring in the closed configuration, taken along the line 7--7
of FIG. 3.
FIG. 8 is a side elevational view of the refuse container base.
FIG. 9 is a top plan view thereof.
FIG. 10 is a cross-section view thereof, taken along the line
10--10 of FIG. 8.
FIG. 11 is a bottom plan view of the refuse container lid.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring initially to FIGS. 1, the subject invention will be
described in the context of forming a refuse container 10 for
illustrative purposes. However, the teachings have application in
the manufacture of other hollow objects and products if so desired.
The container 10 is seen to comprise a lid 12 and a container base
14. The base 14 is of cylindrical general shape, having elongate
sidewalls 16 extending between a bottom surface 18 and an upper rim
20. The lid 12 is shown to have a downwardly concave top wall 22
and a dependent peripheral skirt 24.
With reference to FIGS. 2 and 4, the discharge nozzle incorporating
the subject invention comprises a die pin 26 and a die ring 28.
Typical to common blow molding machines, the die ring is mounted to
an extruder head (not shown) and remains stationary. The apparatus
is used to form an elongate tubular preform or parison 30. The
parison 30 is expanded by air outward into its intended shape as
will be explained below.
The die pin 26 is of frustro-conical configuration, having
sidewalls 32 which taper inwardly from top to a circular bottom
surface 34; and a circular top surface 36. A series of spaced apart
elongate channels 38 are formed to extend into the sidewalls 32
from a top channel end 40 at the top surface 36 to a bottom channel
end 42 positioned a distance above the bottom surface 38. The lower
end of the channels 42 tapers upwardly to an annular portion 46 of
the sidewalls 32 that constitutes a shut-off surface, and each
channel has a lower segment 44 below the shut-off surface 46 that
extends to the bottom surface 38 of the die pin 26.
Six peripherally spaced-apart bolt bores 48 project into the bottom
surface 38 of the die pin 26 to the top surface 36, and a center
bore 50 extends along the major axis of the die pin 26. Four
set-screw access bores extend through the die pin 26 and surround
the center bore 50 as shown in FIG. 4. The die pin is machined from
steel and is configured for attachment to a hydraulic piston (not
shown) on the extruder head that moves the die pin axially in a
reciprocating manner. The configuraton of the die pin 26, except
for the bifurcated channels 42, and its operation in conjunction
with the die ring is conventional and known to those skilled in the
art of blow molding apparatus.
Referring next to FIGS. 2 and 3, the die ring 28 has a general
doughnut shape, defined by cylindrical sidewalls 54 that extend
from a bottom surface 56 to a top surface 58. A center bore 60
extends through the ring 28, defined by bore sidewalls 62 which
taper inwardly from top to bottom to complement the taper of the
die pin surfaces 32. Eight peripherally spaced-apart bolt holes 64
extend through the die ring 28 by which the die ring is bolted to
the extruder head and rendered stationary. The representative
parison 30 is of tubular configuration, having outward sides 66 and
an inward surface 68. Spaced apart ribs 70 extend from the inward
surface 68 into the parison bore from a top parison end 72 to a
bottom parison end 74. The parison 30 is open-ended at the top and
bottom.
As illustrated in FIGS. 2, 3, 6, and 7, the die pin 26 is adapted
to seat within the die ring 28, with sidewalls 32 of the pin 26 in
close proximity to the sidewalls 54 of the die ring 28. An annular
orifice is created between the die pin and the die ring by the gap
therebetween, preferrably 0.045 to 0.100 thousandths of an inch,
depending on the item that is being molded. The die ring 28 is
fixedly bolted to the extruder head (not shown) in conventional
fashion, and the die pin 26 is mounted to a reciprocating hydraulic
piston (not shown) in conventional manner so as to axially move
within the die ring 28 between an upward, open position represented
in FIG. 6 and a downward, closed position represented in FIG. 7.
The frustro-conically shaped die pin 26 and the ring 28 have
matingly sloped adjacent walls that diverge from each other in the
open position to form an annular orifice surrounding the die pin
26.
FIG. 6 illustrates the die pin in the open condition, with an
annular orifice 80 formed between the pin and die ring. After
formation of the parison, the die pin is hydraulically lowered to
the position in FIG. 7 until the shut-off surface 46 contacts the
sidewalls 62 of the die ring and shuts off the orifice 80. To
initiate the cycle again, the die pin is hydraulically raised and
the flow of plastic re-commences to form a new parison. It should
be noted that in the closed, shut-off position of FIG. 7, that
channel segments 44 lie below the shut-off surface 46 and below the
lower edge of the die ring. The segments 44 allow for the expansion
of plastic into rib formation as will be explained below.
FIG. 5 illustrates the injection of molten plastic 76 through the
orifice defined between the die pin 26 and the die ring 28, and out
of the bottom of the die pin to form the parison 30. The channels
38 are bifurcated into an upper portion above the shut-off surface
46 and a smaller lower segment 44 below surface 46. As the plastic
flows over the die pin, it fills the orifice 80 and emerges from
the bottom under pressure. The channel segments 44 below the
shut-off surface 46 create ribs 70 along the inward parison surface
68 from top to bottom; each rib extending parallel and spaced apart
from ribs on either side thereof.
The plastic expands under pressure into the channel segments 44 as
it exits from the bottom of die pin 26, creating a thicker rib than
that created at the upper channel portions. Were a continuous
uninterrupted channel and placing the shut-off surface at the
extreme bottom of the die pin, the thickness of the rib would be on
the order of 0.060 inches. However, by bifurcating each channel and
providing channel segments 44 below the shutoff surface for
expansion of the plastic as it exits the die pin, it has been found
that the thickness of the ribs can be increased by 0.020 inches,
creating ribs having a total thickness of 0.080 inches. The thicker
the ribs, the more strength they will add to the resulting hollow
article wall stock.
The parison sidewall thickness is controlled by the orifice width
between the die pin and die ring, and is preferrably controlled to
be 0.070 inches between the ribs. Conventionally blow molded
containers typically have a nominal wall thickness of 0.060 to
0.080 inches. Thus, it will be understood that while the
(relatively wide) connective wall segments between the ribs of the
subject container are of thinner stock than conventional
containers, the (relatively narrow) ribs are substantially greater
in sectional dimension than conventional containers. The net result
is a 10 percent savings in material usage.
Pursuant to conventional blow molding processes, the parison 30 is
formed between an open mold that is closed simultaneous with die
pin action. The die pin is placed into the down, or closed,
position, blocking further plastic from flowing. Air is then
injected into either the top or bottom ends of the parison, or
both, causing the parison to expand outwardly against the mold
surfaces. The expansion of the parison causes an expansion of the
ribs 70 and thins the wall stock thickness. After the plastic
cures, the mold is opened and the part is ejected.
The lid 12 and base 14 components of the subject refuse container
are formed from the same parison. After the parison expands, cures,
and the part is ejected, the part is separated into the lid and
base components. FIGS. 1, 9, 10, and 11 illustrate the appearance
of the components 12,14 subsequent to their separation. It will be
noted that the ribs 70 have expanded into a diverging formation
from the ends of the original parison.
Also, the ribs 70 are visible only from the interior of the
container and lid and cannot be seen from outside of the
components. This affords the designer of products with the
capability of designing the exterior of the container into any
desired form and placing the reinforcement ribs along the interior,
unseen, portion of the article. The result is an unparalleled
flexibility in the design of blow molded articles.
It should be noted that the subject channeled die pin may be
retrofitted to existing state of the art blow molding equipment
without requiring expensive alterations. Since the die pin does not
affect the operation of the equipment, no expensive changes need be
made to the extruders or the extruder head. Incorporation of the
subject invention into conventional apparatus is thus easily and
inexpensively accomplished.
The thick ribs along the interior of the lid and base components
give rigidity and strength to the article. Thus, while the
connective portions of the side walls of the present invention are
thinner than in comparable blow molded containers, the presence of
the ribs make the containers of the subject invention feel more
rigid and substantial. The ten percent reduction in part weight
that the ribs and thinned connective wall stock gives is,
therefore, accomplish without sacrificing strength or aesthetic
feel. To the contrary, the container is stronger and has a more
rigid and substantial feel due to the presence of the reinforcement
ribs.
Finally, it will be appreciated that the use of the subject
invention does not affect the cycle time of the blow molding
process or add any inefficiency to that process. The formation of
ribs is accomplished by channels in the die pin without affecting
other elements of the apparatus or the process. The added cost of
producing channelled die pins is not substantial and is far less
than the savings achieved by the practice of the invention.
While the above describes the preferred embodiment of the invention
and is particularly related to refuse containers, the subject
invention is not intended to be so limited. Any blow molded article
can be improved by the application of the subject principles. Other
embodiments or applications of the teachings of the subject
invention, which will be apparent to those skilled in the art, are
intended to be within the scope and spirit of the invention.
* * * * *